<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="../js/vue.js"></script>
</head>
<body>
    <div id="app">
        <!-- <p>{{cityName}}</p> -->
        <input type="text" v-model="cityName"/>
    </div>
    <script>
        new Vue({
            el: '#app',
            data: {
                cityName: 'shanghai'
            },
            watch: {
                cityName (newName, oldName) {
                    console.log(newName, oldName)
                    // 应用于：监听某个值，从而改变其他值
                }
            }
        })
    </script>
</body>
</html>